UID/GID fix for kippo

Not sure why trying the same thing as https://github.com/NixOS/nixpkgs/blob/db12d783ffd753145119c22a34ca5945e9a7a4ce/nixos/modules/services/monitoring/munin.nix and https://github.com/NixOS/nixpkgs/blob/f21abed131198355b7623613472dd30330155d28/nixos/modules/services/misc/dictd.nix with config.ids.uids.kippo does not work.